STATE HOUSE — Federal nuclear industry regulators said Wednesday they will increase oversight of the Pilgrim Nuclear Power Plant in Plymouth after inspectors raised concerns about findings associated with the performance of a safety relief valve.

The Nuclear Regulatory Commission’s (NRC) new findings stem from a special inspection at the plant, which is owned by Entergy, following its unplanned shutdown in January.

The NRC in 2013, citing other unplanned shutdowns at Pilgrim, assigned the plant a Degraded Cornerstone Column, or Column 3, designation. The action announced Wednesday moves the plant into a Repetitive Degraded Cornerstone Column, or Column 4, designation on the agency’s “action matrix.”

Federal regulators following an inspection in December 2014 found that Entergy had not adequately identified the causes of the 2013 shutdowns and also raised concerns about some corrective actions. Inspectors in May then found that the issues had been “satisfactorily addressed,” according to the NRC, but also identified the new finding regarding the plant’s safety relief valve.

Entergy could have prevented problems in January associated with safety relief valves by “identifying, evaluating and correcting a condition that caused one of the valves to fail to operate correctly after a plant shutdown on Feb. 9, 2013,” the NRC said, and failing to identify and correct the valve condition constituted a violation of the NRC requirements.

In a statement, NRC Region 1 Administrator Dan Dorman said the most recent finding “highlights the continuing weaknesses in the implementation of Entergy’s program for identifying, evaluating and resolving problems at Pilgrim.” Dorman said, “Our increased oversight will focus on understanding the reasons for those weaknesses and the actions needed to achieve sustained improvements.”

The NRC will also “determine the need for additional regulatory action and examine the extent of equipment, human performance and procedure quality issues that have contributed to or complicated the unplanned shutdowns in 2013 and 2015.”

Entergy Wholesale Commodities President Bill Mohl said Entergy “will review the details of the NRC’s decision to consider what actions we need to take to enable Pilgrim Station to return to normal NRC oversight. While we are confident that Pilgrim continues to be a safely operated plant with highly professional and well-trained employees, we will review all the information and feedback provided by the NRC in order to continue to enhance our performance at the station.”

Mohl said Pilgrim had “previously addressed all of the issues with the Safety Relief Valve since the NRC first issued its preliminary white finding and the plant is operating safely. There was no safety consequence as a result of the problematic Safety Relief Valve issue.”

The NRC concluded there “was an increased likelihood that the valves would not properly function when needed.” The agency said all of the safety relief valves were replaced with valves of a different design during a refueling and maintenance outage at the plant this spring.

Citing “multiple and repetitive safety problems,” Sen. Edward Markey and Attorney General Maura Healey on Wednesday issued statements urging increased oversight at Pilgrim. They cited three automatic shutdowns this year, including an Aug. 23 shutdown that is being investigated by the NRC.

Healey noted her office has called for increased safety measures at Pilgrim, including long-term storage solutions for spent nuclear fuel. “Today’s decision is a disturbing development, and my primary concern is with the safety and well-being of the residents of Massachusetts, particularly those who live near Pilgrim. Entergy must act swiftly and decisively to correct these issues and restore the public’s trust in its ability to safely operate this plant,” she said in a statement.

Markey said he had raised concerns about Pilgrim’s operations and security preparedness “for decades,” and said Pilgrim features the same design as the nuclear reactors that melted down in Fukushima. He said Entergy operated “all three reactors that are currently in NRC’s least safe ‘column 4.'”

“I have repeatedly expressed concern that NRC has prohibited its own staff from asking Entergy to prove that it has the financial resources necessary to operate its reactor fleet safely, and I again urge NRC to revisit its unwise decision to ignore the possibility that Entergy is systematically shortchanging safety,” Markey said.

The Malden Democrat also said Entergy should be required to pay for the distribution of the anti-radiation drug potassium iodide to any Massachusetts community that requests it. The drug can prevent thyroid cancer caused by the release of radiation during a meltdown, he said.

According to Entergy, on Saturday, Aug. 22 at about 4:30 p.m., with the reactor at 100 percent power, Pilgrim Station experienced an automatic shutdown “due to the closure of a single main steam isolation valve.” There are four main steam lines that carry steam from the reactor to the turbine-generator, Entergy said, and the valve automatically isolates the reactor from the turbine-generator.

Entergy said all of its other plant systems responded to the shutdown as designed and said the cause of the shutdown “resulted from a broken instrument control line” that feeds one of the unit’s four main steam isolation valves. The line was repaired and all other lines were inspected before the unit was returned to service. The plant returned to 100 percent power by 6:30 a.m. on Aug 26.